The plot follows two newlyweds who spy on the Nazis for the British Secret Service during their honeymoon in Europe.
This film marked the end of Crawford's 18-year career with MGM before signing with Warner Bros, and the last for character actor Conrad Veidt who died of a heart attack a few weeks after shooting ended.
In the spring of 1939 in England, Oxford University Professor Richard Myles (Fred MacMurray) and his new bride Frances (Joan Crawford) decide to honeymoon on the continent. Because they are American tourists and therefore "above suspicion," they find themselves commissioned by the British secret service to find a scientist who has developed a countermeasure against a new Nazi secret weapon, a magnetic sea mine. Without knowing his name, what he looks like, or where to find him, the couple look upon the search as adventurous and cross Europe seeking clues from clandestine contacts.
In Paris, Frances is given a hat decorated with a rose as a signal for their first contact, who silently instructs them to go to a café in Montmartre, where an unseen contact plants a tourist guidebook to southern Germany in Richard's coat. The couple notice a series of ink dots on a map in the book that linked together form a musical staff with the opening notes to the song "My Love Is Like a Red, Red Rose," which they deduce is their password. Three pinpricks in the same map direct them to the book's seller, A. Werner (Felix Bressart), in Salzburg. Werner informs them they must go to a certain museum where a man named Count Hassert Seidel (Conrad Veidt), calling himself a "guide," suggests that they check into a guest house run by Frau Kleist (Johanna Hofer). She provides them with a book on Franz Liszt with annotations that reveal their next stop should be the village of Pertisau in the Tyrol, where they should inquire about a doctor who collects chess pieces.
Some days later, the couple intends to go to a performance of Liszt but are advised against it by Thornley (Bruce Lester), a fellow houseguest and recent graduate of Oxford. They go anyway; and, during the same loud passage that Thornley had been practicing earlier in the night, a Nazi Colonel, the Commandant of Dachau concentration camp, is shot and killed. Officials insist on questioning the entire audience, but Richard and Frances are rescued by Gestapo Chief Count Sig von Aschenhausen (Basil Rathbone), a former Oxford schoolmate of Richard's. Thornley later admits to Richard that he killed the Nazi as revenge for torturing and killing his Austrian fiancée. He also warns Richard that Thornley and his fiancée had once also been "above suspicion."
Frances and Richard go to the home of the chess collector, Dr. Mespelbrunn (Reginald Owen); but, while he does not seem to be present, Count von Aschenhausen is. They notice sheet music for "My Love Is Like a Red, Red Rose" on his piano, but Sig does not respond to an identification signal that Richard gives him, and the couple becomes suspicious. They hear thumping noises upstairs and discover that Sig is holding Mespelbrunn prisoner. Mespelbrunn tells them to run and that the Gestapo is coming after them. The couple leaves the house just in time, and Hassert appears to help them free Mespelbrunn, who is the missing scientist "Dr. Smith". All four head for Innsbruck, and Mespelbrunn gives Richard the plans for the countermeasure.
The couple obtain counterfeit passports from an elderly couple named Schultz. Richard and Frances in disguise are to catch the train to Milan at separate stations; but, when the Schultzes are arrested by the Gestapo, the police are on the lookout for them. Frances is detained and questioned by the Gestapo; but Thornley, in Innsbruck as well to catch the same train, is able to find Richard. Richard, Thornley, and Hassert sneak in to where Frances is being held and kill all her captors, including Sig; but Thornley is also killed. After fooling the Nazi border guards, Hassert and the newlyweds finally find freedom in Italy.
Variety wrote, "Both MacMurray and Miss Crawford completely handled their roles, despite drawbacks of script material", and T.S. in the New York Times commented, "Joan Crawford...is a very convincing heroine."
Critic Howard Barnes wrote in The New York Herald Tribune that "There are so many floral, musical and cryptographical passwords in the film's plot that the whole show becomes a sort of super treasure hunt... Unfortunately, neither Joan Crawford nor Fred MacMurray looks quite bright enough to unravel the tangled skeins of this screen melodrama."
The film was released on Region 1 DVD on April 6, 2010 from the online Warner Bros. Archive Collection.